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Building my own Tube head

#21
rakirksey said:
My comments did suggest an all-tube amp. IMHO based on some limited experience building somewhat functional tube amps basically from scratch with only a circuit, an all-tube amp is probably less complex than a hybrid amp.

Officially you could build a single-ended low power tube amp with a single preamp tube and a single power tube (This happens to be the circuit for the Invalid Link Removed).

I was just trying to give the OP some suggestions that would end up with higher probability of success. As far as killing oneself a hybrid amp is equally dangerous. It's high current instead of high voltage.
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Voltage is what causes current to flow. Ohm's Law and all that.

I agree with you about complexity, but would go further and say that bass power amp construction is simply not worthwhile as a home project except as an exercise in craftsmanship. For the non-expert there's not much to do except copy established circuits. On the solid state side, I have noticed that published schematics for DIY power amps often contain minimal or no overload protection circuitry. More than half of solid state power amp design is keeping the other half from self destructing.

An exception would be a "chip amp" such as the LM3886, which would get you up into practice amp power levels with minimal complexity. +1 about www.diyaudio.com

And of course there may be a small handful of designers in the world capable of confidently designing a switchmode bass amp.
 
#24
A much easier way to get the B+ is to use a 12V transformer in reverse. Feed it from a 12V 1A AC wall wart. Use a 2A bridge rectifier on the same supply and a simple 7805 regulator wired as a constant current source to supply the heater with 150mA. Another bridge on what should have been the primary and you have your B+. Use a transformer with two 120V primaries series connected will get you about 250V DC.

Paul
 
#25
BassmanPaul said:
A much easier way to get the B+ is to use a 12V transformer in reverse. Feed it from a 12V 1A AC wall wart. Use a 2A bridge rectifier on the same supply and a simple 7805 regulator wired as a constant current source to supply the heater with 150mA. Another bridge on what should have been the primary and you have your B+. Use a transformer with two 120V primaries series connected will get you about 250V DC.

Paul
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What a good idea Paul, had not seen reversed power transformers for many years. Novel way to produce HT. Been a "current" man myself for many decades, like ( very much ) your CC to the heaters, what a great idea! Been wondering how to limit inrush on heaters, to prolong life of tubes.

Part of the ( suggested ) exercise for this student was to introduce the mix of old and new technology, the switcher part was the modern exercise, the tube you can "see" whats going on inside, think young students would get a kick seeing something glowing in the dark(ages)... Well suggested on the gain stage mods, also i was hoping the student would see the possibility to overdrive the stage...Regards John
 
#26
The trouble with the SMPS is the transformers availability in your own country. The original design is from OZ. It is indeed a simple circuit. I have a transformer company in the city who do custom work for a reasonable price. I've got them to build me a suitable toroid that is less than an inch and a half. it will therefor wit within a standard 1U case.

Paul
 
#28
Fair comment Seamonkey. Switch mode supplies are, to me, somewhat of a black art. I've repaired a few, more by luck than good management. I have to admit that the supply in question is elegant in it's simplicity but my earlier comment still stands. Where do you find the transformer. Another thing is how much current will the said circuit supply?

Paul
 
#29
BassmanPaul said:
Fair comment Seamonkey. Switch mode supplies are, to me, somewhat of a black art. I've repaired a few, more by luck than good management. I have to admit that the supply in question is elegant in it's simplicity but my earlier comment still stands. Where do you find the transformer. Another thing is how much current will the said circuit supply?

Paul
Click to expand...

Hello Paul, Seamonkey, Without draging this off topic too much.

The magnetics for the switcher i will check on. This magazine and many others very often give details about winding your own magnetics. Actualy something that can be done at home with simple equipment winding your own transformers or chokes.

Paul, been fortunate to have designed switchers up to 2-300watts. Was steep learning curve as with many things, including bass playing.
Worked on switchers to 4MVA ( not a misprint ). We all start somewhere, and possibly the OP is an exceptional student whom could carry off a full power amplifier project, something only he and his assisting teachers can assess. Your not adverse to helping out with well thought out replies to others on other topics, each time you make a difference to someones learning success. Sometimes that outcome is a long time coming, patience is a fundamental when teaching, as we both know.

Having someone wind your magnetic is very good, though no matter whom was available, i would insist the student calculate and wind his own magnetics. He/she can then spec the production component with confidence.

Regards to all, John
 
#30
Hi Mr. Paul
I suppose if you buy the original article it will tell you how to wind the transformer.
If you look you can see a little tiny picture here, second row:
[Invalid or Expired Link Removed]

12turns and 80turns on a pair of low cost cores and a bobbin,
Invalid Link Removed

It can't be too hard.

It might mention the current available, but I'm guessing it's at least enough for the pre-amp it's designed for.
 

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